This invention relates to absorbent materials having improved multifunctional absorbent properties. More specifically this invention relates to absorbent fibrous composites having rapid fluid intake, improved fluid distribution, and high saturation capacity. This invention also relates to a process for making the absorbent materials.
Various absorbent materials and structure are known in the art. Important characteristics of commercial absorbent materials and structures include fluid intake, fluid retention, and fluid distribution. Known absorbent materials and structures often exhibit at most two of these desired characteristics and are weak in the others. Nonwoven surge materials, as taught in U.S. Pat. No. 5,490,846 to Ellis et al. and in U.S. Pat. No. 5,364,382 to Latimer, for example, have excellent intake functionality but almost no fluid distribution and retention properties. Uncreped through air-dried tissue (UCTAD) material, typically a tissue made from natural fibers such as wood pulp, has a high density providing superior fluid distribution capabilities but poor fluid intake and retention. Current diaper absorbent cores comprising an absorbent fluff and superabsorbent material combination provide good fluid absorbency but, depending on the core density, poor fluid intake and/or distribution. A higher density absorbent core improves distribution but sacrifices fluid intake but a low density absorbent core improves fluid intake and sacrifices distribution.
A typical disposable absorbent product generally has a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. In current commercial absorbent structures layers of different materials, such as a surge layer and an absorbent core layer, are required to provide desired fluid handling characteristics. The result is a bulky absorbent article with many production steps and high cost. There is a need for an absorbent material having combined rapid fluid intake, increased fluid retention, and efficient fluid distribution characteristics.
The use of water-swellable, water-insoluble superabsorbent materials in a fibrous matrix as an absorbent core is well known in the art. As an alternative to superabsorbent containing fibrous matrix absorbent cores, absorbent foams are also known. Absorbent foams generally have lower absorbency rates and can have poor liquid distribution properties. This is typically due to physical characteristics of the foam structure, including discontinuous pore channels, a too large average cell size, unacceptably wide cell size distribution, and/or capillary diameters that vary widely and randomly.
U.S. Pat. No. 6,261,679, issued Jul. 17, 2001 to Chen et al. teaches absorbent fibrous structure that are foam-like, wherein the structure is primarily composed of hydrophilic fibers which serve in part as struts between the open cells. The fibrous structure provides many significant benefits. However, lack of significant amounts of superabsorbent materials in the absorbent structures of U.S. Pat. No. 6,261,679 leaves a need for improved, more absorbent fibrous structures.
There is a need for an absorbent structure having rapid fluid intake, increased fluid retention, and efficient fluid distribution characteristics.
This invention relates to absorbent fibrous foam composites having improved fluid handling properties and methods of making the absorbent fibrous foams. The absorbent fibrous foam composites of one embodiment of this invention have a fluid intake capacity of at least 15 g fluid/g composite, a vertical wicking distance of at least 10 cm, and an absorbency under zero load value of at least 15 grams fluid per gram composite. The absorbent fibrous foam composites of another embodiment of this invention have an intake rate of at least 1.9 cc liquid/second at 80% composite saturation and a liquid lockup fraction of at least about 0.75 at 50% superabsorbent saturation.
The low-density absorbent fibrous foam composites of one embodiment of this invention include a water-insoluble fiber and a superabsorbent material. The superabsorbent material has a weight amount between about 10 to 70 weight percent and the water-insoluble fiber has a weight amount between about 20 to 80 weight percent, wherein weight percent is based on total weight of the absorbent composite.
The low-density absorbent fibrous composite of one embodiment of this invention includes a water insoluble fiber, a superabsorbent material, and a binding agent. The binding agent constitutes about 0 to 10 weight percent, based on total weight of the absorbent composite. The binding agent is used to bind the fibers together and provides excellent wet and dry strength. In one embodiment the superabsorbent material can also act as a binding agent.
One embodiment of the invention is a freeze-dried absorbent fibrous foam. The freeze-dried absorbent fibrous foam is made by forming a slurry comprising water, a water-insoluble fiber, and a binding agent. An absorbent material having a slow absorption time, or a surface treated fast absorption material, is then added to the slurry. The slurry has to be formed into a uniform sheet while enough interstitial fluid is still present or the slurry is still flowable. The slurry is cooled to a temperature between about xe2x88x9250xc2x0 C. and 0xc2x0 C. at a cooling rate effective to freeze the water. The frozen water is removed through sublimation and a fibrous absorbent foam is recovered.